NGC 6888 - The Crescent Nebula in Bi-Color
Date: August 17, 2020
Cosgrove’s Cosmos Catalog ➤#0047
NGC 6888 - The Crescent Nebula that was created with mixed Ha and OIII data. (click to enlarge)
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About the Target
NGC 6888, the Crescent Nebula. Found in the constellation Cygnus the Swan, The Crescent Nebula is an emission nebula located 5,000 light-years away.
The Annotated Image
The annotated image was created using Pixinsight’s ImageSolver and AnnotateImage scripts.
The Location in the Sky
IAU/Sky & Telescope Constellation Chart for Cygnus, showing the Crescent Nebula’s location indicated by a yellow arrow.
About the Project
I first shot this object about a year ago (2019). I was excited about what I got then, and I wanted to see what I could do with a little more experience under my belt.
This is was shot with a cooled monochromatic camera and Ha and OIII narrowband filters and processed as a Bi-Color image. Bi-color images are created by taking the results of two color filters and creating a false-color RGB image.
This is only the third image I have made with my mono camera. The first two images were LRGB images, so this is the first tie That I am attempting to use narrowband filters. This restricts a lot more light and requires much longer exposures -both for sub and everything else - including the exposures used for auto-focus runs.
This was also the first time that I've done a Bi-Color image. I am still learning all of this fun stuff, so I expect to improve on the processing of this as I learn more…
Previous Effort
I have shot this target once before - just after getting my first telescope platform working. You can see that post HERE.
Here are the images side-by-side for comparison:
My first effort, back in August of 2019 (click to zoom)
THe current Project results. (Click to Zoom)
Capture Details
Light Frames
15 x 300 seconds Ha
13 x 300 seconds OIII
Total of 2.3 hours
Cal Frames
50 x 2 seconds Bias exposures
25 x 300 seconds Dark exposures
50 Ha Flats
50 Oiii Flats
Capture Hardware
Scope: Astrophysics 130mm Starfire F/8.35 APO refractor
Guide Scope: Televue 76mm Doublet
Camera: ZWO ASI1600mm-pro with ZWO Filter wheel with ZWO LRGB filter set, and ZWO GeII 7nm Narrowband filter set
Guide Camera: ZWO ASI290Mini
Focus Motor: Pegasus Astro Focus Cube 2
Mount: Ioptron CEM60
Polar Alignment: Polemaster camera
Software
Capture Software: PHD2 Guider, Sequence Generator Pro controller
Image Processing: Pixinsight, Photoshop - assisted by Coffee, extensive processing indecision and second-guessing, editor regret and much swearing…..
Over the winter, I began to get things ready for the second platform. Clearly I had some work to do. I needed to determine what I was going to do for a camera, and I needed to determine what to do get the mount functioning at the precision needed.